Field effect transistor and method for manufacturing the same

ABSTRACT

A method for manufacturing a field effect transistor, includes: forming a mask of an insulating film on a semiconductor layer containing Si formed on a semiconductor substrate; forming the semiconductor layer into a mesa structure by performing etching with the use of the mask, the mesa structure extending in a direction parallel to an upper face of the semiconductor substrate; narrowing a distance between two sidewalls of the mesa structure and flattening the sidewalls by performing a heat treatment in a hydrogen atmosphere, the two sidewalls extending in the direction and facing each other; forming a gate insulating film covering the mesa structure having the sidewalls flattened; forming a gate electrode covering the gate insulating film; and forming source and drain regions at portions of the mesa structure, the portions being located on two sides of the gate electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-262344 filed on Oct. 5, 2007in Japan, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a field effect transistor and a methodfor manufacturing the field effect transistor.

2. Related Art

Conventionally, the driving current per unit gate length is increased byreducing the gate length of each transistor and thinning each gateinsulating film, so as to form more sophisticated CMOS circuit deviceswith higher performance. In this trend, the transistor size that canobtain the necessary driving current has become smaller, and highintegration can be achieved. At the same time, the driving voltage hasbecome lower, and the power consumption per unit device can be reduced.

However, as the gate lengths have become smaller, the technical hurdlethat needs to be crossed to achieve higher performances is rapidlybecoming higher. To counter this difficult situation, a structureincluding two or more gate electrodes is effective. For example, adouble-gate structure having gate electrodes above and below thechannel, and a gate-all-around structure that has gate electrodessurrounding the channel are effective. Among gate-all-around structures,those with channels having diameters of 10 nm or less are also known asnanowire transistors. Structures each having a gate formed at eitherside of the channel (fin) of a mesa structure that is perpendicular tothe substrate and has a plate-like shape are called Fin FETs, andstructures each having a gate formed on each of the three faces (the twosidewalls and the upper face) are called tri-gate FETs. Those structuresare collectively called multi-gate structures. By virtue of the gates,each of those structures has greater electro-static controllability ofthe channel carriers than that of a regular planar-type single-gatestructure. Thus, those structures can effectively prevent theshort-channel effects even when the impurity concentration in thechannels is restricted to a low value.

Only with a single multi-gate channel, the ON current per FET occupationarea might not exceed the ON current of a regular planar-type MOSFET.Therefore, there has been a structure in which multi-gate channels arestacked in the vertical direction to obtain a sufficient ON current (seeT. Ernst, et al., IEDM Tech. Dig., 2006/IEDM.2006.346955, for example).According to T. Ernst, et al., IEDM Tech. Dig., 2006/IEDM.2006.346955,Si layers and SiGe layers are alternately stacked in advance, and RIE(Reactive Ion Etching) is performed to form fins and mesas. After that,selective etching is performed to remove only the SiGe layers from thesidewalls.

The channels of those multi-gate MOSFETs are normally formed with mesastructures or fins formed on a SOI substrate or a bulk Si substrate by alithography technique and RIE. Here, there exist two technicalproblems: 1) size and shape variations are caused; and 2) the widths offins need to be reduced to approximately 10 nm or less, which is smallerthan the limit in terms of lithography.

The problem of variations as the first problem can be divided into twofactors. One is the shape and size variations in the plane of thesubstrate. The shape and size variations are caused due to the linewidth variation caused by the lithography and line edge roughness (LER).The other factor concerns the variation in the shapes of cross sectionsperpendicular to the substrate, and is caused by the variation in mesawidth in the vertical direction caused by RIE. The width variationsresult in variations in electric characteristics such as thresholdvoltages, and the uneven surfaces of the sidewalls cause an increase incarrier scattering and a decrease in driving current.

To avoid the adverse influence, there are reported cases wherehigh-temperature annealing was performed on Fin FETs having Si channelsin a hydrogen atmosphere after RIE was performed. For example, adecrease in leakage by virtue of the hydrogen annealing performed on thesidewalls of Fin FETs has been reported (see W. Xiong, et al., IEEEElectron Device Lett. 25, 541 (2004), for example). This was achieved asthe corners of the cross sections of fins were rounded by the surfacemigration of the Si atoms caused by the hydrogen annealing, and thefield concentration was relaxed. An increase in ON current and areduction in noise have also been reported (see J-S Lee, et al., IEEEElectron Device Lett. 24, 186 (2003), for example). However, thistechnique is also based on the surface flattening effect of the surfacemigration of Si atoms.

To counter the problem of the need to reduce fin widths as the secondproblem, sacrifice oxidation is normally performed. However, it isdifficult to reduce the widths while maintaining the rectangular shapesof the fins, because of the stress in the oxide films and the dependenceof the oxidation rate on the surface orientation.

By a conventional hydrogen annealing technique, however, the crosssections of the sidewalls tend to have round corners due to the surfacemigration. Therefore, the conventional hydrogen annealing technique isnot suitable for controlling the shapes of cross sections of Fin FETshaving smaller fin widths that are required in more minute CMOS.Furthermore, the effect of the hydrogen annealing to reduce the lineedge roughness caused by the lithographic process is not clearlydisclosed as technical information.

In a case where a conventional hydrogen annealing technique is used toform a structure having channels stacked in the vertical direction, thechannel width of each upper layer differs from the channel width of eachlower layer, since the shapes of the etched cross sections are notrectangular, and variations might be caused among the threshold valuesof the channels and the likes.

In a case where SiGe-Fin FETs or nanowire FETs are produced byperforming a Ge-condensation by oxidization process on SiGe fins, the Gecomposition varies with the variation in line width, and variationsmight be caused in ON current and threshold voltage value. Furthermore,there has not been a report that the variation in line width was reducedby flattening the sidewalls of SiGe fins by a conventional hydrogenannealing technique. As described above, to counter the problem of theneed to reduce fin widths, a sacrifice oxide film is normally used.However, it is difficult to reduce the fin widths while maintaining therectangular shapes of the fins, due to the stress in the oxide film andthe dependence of the oxidation rate on the plane direction.

SUMMARY OF THE INVENTION

The present invention has been made in view of these circumstances, andan object thereof is to provide a field effect transistor and method formanufacturing the field effect transistor that has the smallest possiblesize and shape variation among channels and the smallest possiblechannel width.

A method for manufacturing a field effect transistor according to afirst aspect of the present invention includes: forming a mask of aninsulating film on a semiconductor layer containing Si formed on asemiconductor substrate; forming the semiconductor layer into a mesastructure by performing etching with the use of the mask, the mesastructure extending in a direction parallel to an upper face of thesemiconductor substrate; narrowing a distance between two sidewalls ofthe mesa structure and flattening the sidewalls by performing a heattreatment in a hydrogen atmosphere, the two sidewalls extending in thedirection and facing each other; forming a gate insulating film coveringthe mesa structure having the sidewalls flattened; forming a gateelectrode covering the gate insulating film; and forming source anddrain regions at portions of the mesa structure, the portions beinglocated on two sides of the gate electrode.

A method for manufacturing a field effect transistor according to asecond aspect of the present invention includes: forming first andsecond masks of insulating films on first and second semiconductorlayers of Si, the first and second semiconductor layers formed indifferent regions from each other on a semiconductor substrate; formingthe first semiconductor layer into a first mesa structure and the secondsemiconductor layer into a second mesa structure by performing etchingwith the use of the first and second masks, the first mesa structureextending in a first direction parallel to an upper face of thesemiconductor substrate, the second mesa structure extending in a seconddirection parallel to the upper face of the semiconductor substrate;narrowing each distance between two first sidewalls of the first mesastructure and flattening the first sidewalls by performing a heattreatment in a hydrogen atmosphere, the two first sidewalls extending inthe first direction and facing each other, and narrowing each distancebetween two second sidewalls of the second mesa structure and flatteningthe second sidewalls by performing the heat treatment in the hydrogenatmosphere, the two second sidewalls extending in the second directionand facing each other; forming a third mask that covers the first mesastructure and leaves the flattened second sidewalls of the second mesastructure exposed; forming a SiGe film on each of the flattened secondsidewalls of the second mesa structure; performing thermal oxidizationto turn the second mesa structure and the SiGe film into a third mesastructure made of SiGe and a silicon oxide film, the third mesastructure being thinner than the second mesa structure and the siliconoxide film covering sidewalls of the third mesa structure; removing thesilicon oxide film; forming first and second gate insulating filmscovering the first and third mesa structures, respectively; formingfirst and second gate electrodes covering the first and second gateinsulating films, respectively; forming first source and drain regionsat portions of the first mesa structure, the portions being located ontwo sides of the first gate electrode; and forming second source anddrain regions at portions of the third mesa structure, the portion beinglocated on two sides of the second gate electrode.

A method for manufacturing a field effect transistor according to athird aspect of the present invention includes: forming first and secondmasks made of insulating films on a Si layer and a SiGe layer, the Silayer and the SiGe layer formed in different regions from each other ona semiconductor substrate; forming the Si layer into a first mesastructure and the SiGe layer into a second mesa structure by performingetching with the use of the first and second masks, the first mesastructure extending in a first direction parallel to an upper face ofthe semiconductor substrate, the second mesa structure extending in asecond direction parallel to the upper face of the semiconductorsubstrate; narrowing each distance between two first sidewalls of thefirst mesa structure and flattening the first sidewalls by performing aheat treatment in a hydrogen atmosphere, the two first sidewallsextending in the first direction and facing each other, and narrowingeach distance between two second sidewalls of the second mesa structureand flattening the second sidewalls by performing the heat treatment inthe hydrogen atmosphere, the two second sidewalls extending in thesecond direction and facing each other; forming first and second gateinsulating films covering the first and second mesa structures havingthe sidewalls flattened, respectively; forming first and second gateelectrodes covering the first and second gate insulating films,respectively; forming first source and drain regions at portions of thefirst mesa structure, the portions being located on two sides of thefirst gate electrode; and forming second source and drain regions atportions of the second mesa structure, the portions being located on twosides of the second gate electrode.

A field effect transistor according to a fourth aspect of the presentinvention includes: a semiconductor mesa structure on a Si substratehaving a {001} plane as a principal surface, having a rectangularparallelepiped shape, contains Si, having an upper face formed with a{001} plane, and having two sidewalls facing each other and being formedwith {110} planes; a source region and a drain region formed at adistance from each other in a longitudinal direction of the mesastructure; a gate insulating film formed on a portion of the mesastructure, the portion being between the source region and the drainregion; and a gate electrode formed on the gate insulating film, aconnecting portion between each of the sidewalls of the mesa structureand the Si substrate being formed with a {111} plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) to 2(f) illustrate the manufacturing procedures according toa manufacture method of a first embodiment;

FIGS. 3( a) to 3(f) illustrate the manufacturing procedures according toa manufacture method as a modification of the first embodiment;

FIGS. 4( a) to 6(f) illustrate the manufacturing procedures according toa manufacture method of a second embodiment;

FIGS. 7( a) to 7(f) illustrate the manufacturing procedures according toa manufacture method of a third embodiment;

FIGS. 8( a) to 9(f) illustrate the manufacturing procedures according toa manufacture method of a fourth embodiment;

FIGS. 10( a) to 11(f) illustrate the manufacturing procedures accordingto a manufacture method of a fifth embodiment;

FIGS. 12( a) to 13(d) illustrate the manufacturing procedures accordingto a manufacture method of a sixth embodiment;

FIGS. 14( a) to 18(b) illustrate the manufacturing procedures accordingto a manufacture method of a seventh embodiment;

FIGS. 19( a) to 23(b) illustrate the manufacturing procedures accordingto a manufacture method of an eighth embodiment;

FIGS. 24( a) to 27(b) illustrate the manufacturing procedures accordingto a manufacture method of a ninth embodiment;

FIGS. 28( a) to 30(b) illustrate the manufacturing procedures accordingto a manufacture method of a tenth embodiment;

FIGS. 31( a) to 31(c) illustrate an embodiment of the present invention;

FIGS. 32A and 32B show SEM images for explaining the effects of anembodiment of the present invention;

FIGS. 33A and 33B show SEM images for explaining the effects of anembodiment of the present invention;

FIGS. 34A and 34B show SEM images for explaining the effects of anembodiment of the present invention;

FIGS. 35A and 35B show SEM images for explaining the effects of anembodiment of the present invention; and

FIG. 36 illustrates the effects of the modification of the firstembodiment.

DETAILED DESCRIPTION OF THE INVENTION

First, before describing the embodiments of the present invention, thecourse of events for achieving the present invention will be describedbelow.

The inventors conducted various hydrogen annealing experiments on minutemesa structures that were tens to hundreds of nanometers (nm) in heightand width, and were made of Si or SiGe.

More specifically, samples of semiconductor layers that were made of Sior SiGe and each had a (001) plane as the principal surface wereprepared on a substrate, as shown in FIG. 31( a). Hard masks ofinsulating films were formed on the sample semiconductor layers. Withthe use of the hard masks, patterning was performed on the semiconductorlayers by RIE, so as to form mesa structures. Each of the samples hadthe hard mask remaining on the mesa structure.

Next, five mixed gas atmospheres each containing hydrogen gas and Ar gaswith hydrogen gas partial pressures of 100%, 50%, 20%, 10%, and 1% wereprepared. Here, the total pressure of each of those mixed gasatmospheres was the atmospheric pressure (=1.01×10⁵ Pa), and thetemperature was 1000° C. The above described samples were left in themixed atmospheres, and hydrogen annealing was performed for fiveminutes. As a result, the widths of the mesas of the samples subjectedto the heat treatment in the atmospheres with the hydrogen gas partialpressures of 100%, 50%, and 20% became smaller, and a series of flatlow-index planes (such as {100} planes, {110} planes, or {111} planes)appeared on each sidewall of the mesas. The inventors consider that thereduction of the width of each mesa and the appearance of flat low-indexplanes (such as {100} planes, {110} planes, or {111} planes) were causedby virtue of the Si thermal etching with hydrogen rather than by virtueof the flattening effect of the surface migration of Si atoms observedin conventional cases. The etching width is approximately 10 nm to 50 nmfor each sidewall after the etching for several minutes, which iseffective for thinning 50-nm wide fins or mesa structure produced by alithography technique to approximately 10 nm.

However, the above effects were not achieved with the samples subjectedto the heat treatment in the atmospheres with hydrogen gas partialpressures of 10% and 1%.

When the temperature of the mixed gas atmospheres each containing ahydrogen gas was changed to 950° C., the same effects as above wereachieved with the hydrogen gas partial pressures of 100%, 50%, and 20%.

Accordingly, it became apparent that, when hydrogen annealing wasperformed at a higher temperature (950° C. or higher) with a highhydrogen partial pressure (0.2×10⁵ Pa), the sidewalls of each mesa wereetched to reduce the width of the mesa, and flat low-index planes (suchas {100} planes, {110} planes, or {111} planes) appeared on eachsidewall, by virtue of the Si thermal etching effect of hydrogen.

The same effects as above were observed not only in mesas formed withlattice relaxed Si, but in mesas formed with strained Si or SiGe. Theinventors discovered that fin thinning and sidewall flattening could beachieved at the same time by performing hydrogen annealing under theabove conditions on minute mesa structures formed with Si, strained Si,or SiGe.

The above mesa structures were formed by RIE on a SOI substrate thatincludes a supporting substrate made of Si, a buried oxide film (BOX),and a SOI layer having a (001) plane as the principal surface. FIG. 32Ashows a SEM (Scanning Electron Microscopy) image of the mesa structures.After that, hydrogen thermal etching was performed on the mesastructures in an atmospheric-pressure H₂ gas atmosphere at 1000° C. for5 minutes. FIG. 32B shows a SEM image of the mesa structures at thispoint. FIGS. 33A and 33B are SEM images of the mesa structures shown inFIGS. 32A and 32B, seen from the top. As can be seen from FIGS. 32A and33A, the sidewalls of the mesa structures are not flat before thehydrogen thermal etching, and there is a variation in shapes (widths) ofthe mesa structures. However, after the hydrogen thermal etching, thesidewalls of the mesa structures (fins) are substantially perpendicularto the substrate and are flat, and there are no variations in shapes(widths) of the mesa structure (fins), as can be seen from FIGS. 32B and33B. The width variation (3 a) was measured. As a result, the widthvariation 3 a was 7 nm before the hydrogen thermal etching, but was 1 nmafter the hydrogen thermal etching. Here, a is the standard deviation ofthe mesa width.

Also, fins were formed by performing RIE on a bulk Si substrate having a(001) plane as the principal surface. FIG. 34A shows a SEM image of thefins. After that, hydrogen thermal etching was performed on the fins inan atmospheric-pressure hydrogen gas atmosphere at 950° C. for 10minutes. FIG. 34B shows a SEM image of the fins at this point. As can beseen from FIGS. 34A and 34B, the widths of the mesa structures becomesmaller after the hydrogen thermal etching than the widths observedbefore the hydrogen thermal etching. Also, after the hydrogen thermaletching, flat [110] planes that were substantially perpendicular to thesubstrate appeared on each sidewall of the mesa structures (fins). {111}planes also appear at the connecting portion between each sidewall ofthe fins and the surface of the substrate. The reason for the appearanceof the {111} planes will be explained in the description of a sixthembodiment.

Thermal oxidization is further performed on the mesa structures (fins)having flat sidewalls after the hydrogen thermal etching. As a result, ananowire structure with uniform widths and minimum line edge roughnesscan be obtained, as shown in FIG. 31( c).

Further, mesa structures are formed by performing RIE on a semiconductorlayer made of SiGe, with the use of hard masks formed with insulatingfilms. Thermal oxidization (thermal concentration) is then performed onthe mesa structures without and with the hydrogen thermal etching. FIG.35A shows a STEM (Scanning Transmission Electron Microscopy) image ofthe nanowire structures (fins) made of SiGe without the hydrogen thermaletching. FIG. 35B shows a STEM image of the nanowire structures (fins)made of SiGe that are thermally oxidized after subjected to hydrogenthermal etching. As can be seen from FIG. 35A, in the case wherehydrogen thermal etching is not performed, oxidization progresses whilethe width variation remains as before. On the other hand, in the casewhere oxidization is performed after the hydrogen thermal etching,thermal oxidization progresses while the uniformity of the widths of thefins is maintained and the SiGe nanowires having uniform widths areformed.

The present invention has been made based on the above findings, andembodiments of the present invention are described below, with referenceto the accompanying drawings.

First Embodiment

Referring to FIGS. 1( a) to 2(f), a method for manufacturing a fieldeffect transistor in accordance with a first embodiment of the presentinvention is described. FIGS. 1( a), 1(b), 1(d), 2(a), 2(c), and 2(e)are cross-sectional views illustrating procedures to be carried out bythe method for manufacturing the field effect transistor in accordancewith this embodiment. FIGS. 1( c), 1(e), 2(b), 2(d), and 2(f) are planviews. FIGS. 1( b), 1(d), 2(a), 2(c), and 2(e) are cross-sectionalviews, taken along each line A-A of FIGS. 1( c), 1(e), 2(b), 2(d), and2(f).

The field effect transistor manufactured by the manufacture method inaccordance with this embodiment is a Fin FET that has a channel made ofSi.

First, as shown in FIG. 1( a), a SOI substrate 4 having a supportingsubstrate 1, a buried oxide film 2, and a 50-nm thick SOI layer 3 havinga (001) plane as the principal surface is prepared. A 2-nm thick siliconoxide film 5 and a 20-nm thick silicon nitride film 6 are deposited inthis order on the SOI layer 3.

A hard mask 9 formed with a silicon oxide film 5 and a silicon nitridefilm 6 is formed on source and drain portions 7 and a portion 8 by alithography technique using an electron beam or an excimer laser andreactive ion etching (RIE). The portion 8 is to be a channel region.Here, the channel direction (the direction perpendicular to the line A-Aof FIG. 1( c)) is the <1-10> direction, and the width of the hard mask 9at the portion 8 to be the channel region is 40 nm. With the hard mask 9being used as a mask, RIE is performed to form the source and drainportions 7 and the portion 8 to be the channel region into a mesastructure, as shown in FIGS. 1( b) and 1(c). In this embodiment, themesa structure may be a trapezoidal structure having the smaller widthat the upper portion and the greater width at the portion closer to thesubstrate 4 in section, as shown in FIGS. 33( a) and 34(a).Alternatively, the mesa may be a trapezoidal structure having thegreater width at the upper portion and the smaller width at the portioncloser to the substrate 4 in section, or may be a lentoid structurehaving the smaller width at the upper and lower portions than the widthat the center portion, or may be a rectangular structure.

After the native oxide film on each sidewall of the mesa is removed withthe use of diluted hydrofluoric acid, the SOI substrate is subjected to5-minute annealing in a 100%-hydrogen atmosphere with atmosphericpressure (1.0×10⁵ Pa) at 1000° C. As a result, a fin 10 having a flat(110) plane 10 a that is located on each sidewall of the channel portionof the mesa and is perpendicular to the principal surface of thesubstrate 4 is formed as shown in FIGS. 1( d) and 1(e). This is theeffect of etching of the sidewalls (thermal etching with hydrogen) thatis caused as hydrogenated silicon is generated from a reaction betweenhydrogen and Si and vaporizes. Since the etching rate of {110} planes islower than those of the other high-index planes, (110) and (−1-10)planes appear. The etching effect is in a competitive relationship withthe surface migration of Si. To make the etching effect dominant, it ispreferable that the temperature is increased to 950° C. or higher, andthe hydrogen partial pressure is to 0.2×10⁵ Pa or higher. Further, tomaintain the mesa structure, particularly, to maintain the fin structurehaving a high aspect ratio at the channel portion, it is preferable thatthe hard mask 9 is formed on the upper face. If one of thoserequirements is not satisfied, the appearance of {110} planes might notbe observed. After the thermal etching with hydrogen, the width of thefin 10 becomes 18 nm. The width of the fin 10 can be further reduced to10 nm or less by prolonging the etching period. Since the (110) plane 10a appears on each sidewall of the fin 10 to be the channel, eaves 9 aare formed at the lower portion of the hard mask 9, as shown in FIG. 1(d).

Next, as shown in FIGS. 2( a) and 2(b), etching is performed on theeaves 9 a of the hard mask 9 with hot phosphoric acid and dilutedhydrofluoric acid. At this point, the silicon nitride film 6 of the hardmask 9 is not completely removed but is partially left. As shown inFIGS. 2( c) and 2(d), to round the corners of the fin 10, a thermaloxide film 11 is formed on the exposed surface of the fin 10 through30-second rapid terminal oxidization at 1050° C. After that, the thermaloxide film 11 is removed with diluted hydrofluoric acid. As a result,the width of the fin 10 becomes 10 nm.

A gate oxide film 12 made of HfO₂ is then formed to cover the surface ofthe fin 10, and a polysilicon film is further deposited. As shown inFIGS. 2( e) and 2(f), the polysilicon film is patterned by aphotolithography technique, so as to form a gate electrode 13. Theregions of the fin 10 outside the formation region of the gate electrode13 serve as source and drain regions, and connect to the source anddrain portions 7.

A thermal oxide film of 2 nm in film thickness (not shown) is thenformed by RTO on the exposed sidewalls of the fin 10 and at the sideportions of the gate electrode 13. After that, impurity ions (arsenicfor the n-channel, and boron for the p-channel) are injected into thesource and drain portions 7 and the gate electrode 13 made ofpolysilicon. At this point, the SOI substrate is tilted at approximately30 degrees on the channel direction axis, so as to inject sufficientimpurities into the side portions at left and right sides of the fin 10.

A silicon oxide film of 5 nm in film thickness (not shown) and a siliconnitride film of 15 nm in film thickness (not shown) are then depositedby CVD (Chemical Vapor Deposition), and etching is performed on thesilicon nitride film and the silicon oxide film by RIE, so as to formgate sidewalls formed with the silicon nitride film and the siliconoxide film at the side portions of the gate electrode 13. After that,impurity ions (arsenic for the n-channel, and boron for the p-channel)are again injected, and activation is also performed by RTA, so as toform the source and drain regions. In this ion implantation, the SOIsubstrate is also tilted at approximately 30 degrees on the channeldirection axis, so as to inject sufficient impurities into the sideportions at left and right sides of the fin 10.

Lastly, an interlayer insulating film (not shown) is deposited, andcontact holes (not shown) continuing to the source and drain regions andthe gate electrode are formed through the interlayer insulating film.The contact holes are filled with a conductive material to form therespective electrodes. Wires are then formed on the interlayerinsulating film, so as to complete a circuit having the MOS transistor.

In this embodiment, a fin having the {110}-planes sidewalls is formed ona semiconductor substrate having the (001) plane as the principalsurface. However, a fin having sidewalls formed with {110} planesequivalent to (110) planes may be formed on a semiconductor substratehaving a {001} plane equivalent to the (001) plane as the principalsurface. Here, a {001} plane is a comprehensive representation of theMiller's index indicating any of a (001) plane, a (010) plane, a (100)plane, a (00-1) plane, a (0-10) plane, and a (−100) plane. A {110} planeis a comprehensive representation of the Miller's index indicating anyof a (110) plane, a (101) plane, a (011) plane, a (−1-10) plane, a(−10-1) plane, a (0-1-1) plane, a (−110) plane, a (1-10) plane, a (10-1)plane, and a (−101) plane. A {111} plane is a comprehensiverepresentation of the Miller's index indicating any of a (111) plane, a(−111) plane, a (1-11) plane, a (11-1) plane, a (−1-1-1) plane, a(1-1-1) plane, a (−11-1) plane, and a (−1-11) plane. In the following, a( . . . ) plane can be replaced with any plane represented by the {. . .} plane equivalent to the ( . . . ) plane.

The manufacture method can also be used to produce a complementaryMOSFET (CMOSFET) circuit consisting of many p-channel and n-channel FinFETs.

The manufacture method in accordance with this embodiment can be used toproduce a field effect transistor having a fin-like channel patterned inone of the [110] directions on a (001) substrate The manufacture methodin accordance with this embodiment is particularly effective inproducing a p-channel MOSFET to achieve greater driving current, as thesidewalls of the fin are formed with {110} planes having higher holemobility than on the {100} planes.

Other than that, the manufacture method in accordance with thisembodiment can be used to produce a field effect transistor having achannel patterned in one of the [100] directions on a (001) substrate.In such a case, the manufacture method is particularly effective inproducing an n-channel MOSFET to achieve greater driving current, asflat {010} planes appear on each sidewall of the fin.

The manufacture method can also be used to produce a field effecttransistor having a channel in the <−110> direction on a (110)substrate. In such a case, the manufacture method is particularlyeffective in producing an n-channel MOSFET to achieve greater drivingcurrent, as flat {001} plane appears on each sidewall of the fin.

The manufacture method can also be used to produce a field effecttransistor having a channel patterned in the <−112> direction on a (110)substrate. In such a case, flat {111} planes appears on each sidewall ofthe fin, and therefore, the same driving current can be achieved in botha p-channel MOSFET and an n-channel MOSFET. Thus, the circuit designbecomes simpler.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <001>direction on a (110) substrate. In such a case, the manufacture methodis particularly effective in producing a p-channel MOSFET to achievegreater driving current, as flat {110} planes appear on each sidewall ofthe fin.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the [−211]direction on a (111) substrate. In such a case, the manufacture methodis particularly effective in producing a p-channel MOSFET to achievegreater driving current, as flat {011} planes appear on each sidewall ofthe fin.

In this embodiment, if a SOI substrate including a SOI layer that is asilicon layer having tensile strain in the plane (a strained SOIsubstrate) is used, a Fin FET having tensile strain in the channeldirection is formed through the same procedures as above. In such acase, the electron mobility becomes high by virtue of the uniaxial stainin the channel direction, and particularly, the ON current of ann-channel MOSFET becomes higher.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

(Modification)

Referring now to FIGS. 3( a) to 3(f), a method for manufacturing a fieldeffect transistor in accordance with a modification of this embodimentis described. FIGS. 3( a), 3(c), and 3(e) are cross-sectional viewsillustrating procedures to be carried out by the method formanufacturing the field effect transistor in accordance with thismodification. FIGS. 3( b), 3(d), and 3(f) are plan views. FIGS. 3( a),3(c), and 3(e) are cross-sectional views, taken along each line A-A ofFIGS. 3( b), 3(d), and 3(f).

By the manufacture method in accordance with this modification, the sameprocedures as those of the first embodiment illustrated in FIGS. 1( d)and 1(e) are carried out. More specifically, the same procedures asthose procedures for performing thermal etching with hydrogen arecarried out so as to form the fin 10 having a (110) plane 10 a on eachsidewall of the mesa structure and the eaves 9 a in the hard mask 9.

After that, the hard mask 9 is completely removed, as shown in FIGS. 3(a) and 3(b). One-minute rapid thermal oxidization is then performed at atemperature between 1050° C. and 1200° C., more preferably at 1100° C.,so as to form a thermal oxide film 11 on the surface of the fin 10, asshown in FIGS. 3( c) and 3(d). Through the thermal oxidization, thesidewalls are formed into convex-lens shapes including planes tiltedwith respect to a (110) plane (such as a (311) plane and a (111) plane)(see FIGS. 3( c) and 3(d)). After that, the thermal oxide film 11 isremoved with diluted hydrofluoric acid, so as to expose the fin 10. As aresult, the fin 10 is put into a floating state above the buried oxidefilm 2.

A gate oxide film 12 made of HfO₂ is then formed to cover the surface ofthe fin 10, and a polysilicon film is further deposited. Patterning isthen performed on the polysilicon film by a photolithography technique,so as to form a gate electrode 13, as shown in FIGS. 3( e) and 3(f).

The procedures after that are the same as those of the first embodiment.As a result, the channel become nanowires that form two {100} planes onthe upper face and the lower face, and two sidewalls having the shapesof convex lenses.

Accordingly, the contribution of the (110) plane having the lowestelectron mobility can be reduced. By applying this method to ann-channel transistor, the driving current can be made higher than thedriving current of a Fin FET that has a channel having sidewalls on(110) planes. Also, as the channel has a gate-all-around structurecompletely covered with the gate, the OFF current can also be reduced.

FIG. 36 shows the result of measurement of the electron mobility in ananowire channel having two sidewalls in the form of convex lenses as inthis modification (indicated by graph g₁), and the result of measurementof the electron mobility in a nanowire channel having two flat sidewalls(indicated by graph g₂). The temperature at the time of measurement is300 K. The channel is formed with strained Si, and includes 500nanowires each having a channel length L of 20 μm and a channel width Wof 27 nm. The abscissa axis indicates the value of averaged surfacecarrier density, Ns (cm⁻²), obtained by dividing the number of carriersin the channel by the surface area of the channel, and the ordinate axisindicates the electron mobility. The shapes of the sidewalls of thenanowires are controlled by adjusting the thermal oxidizationtemperature after the 5-minute hydrogen thermal etching in hydrogen gaswith atmospheric pressure at 1000° C. The thermal oxidizationtemperature is 1100° C. in the case of graph g₁, and is 1050° C. in thecase of graph g₂. As can be seen from FIG. 36, in the generally used Nsrange (1×10¹² cm⁻² to 10×10¹² cm⁻²), the electron mobility in thenanowire channel having the two sidewalls in the form of convex lensesis higher than the electron mobility in the nanowire channel having theflat sidewalls.

Second Embodiment

Referring now to FIGS. 4( a) to 6(f), a method for manufacturing a fieldeffect transistor in accordance with a second embodiment of the presentinvention is described. FIGS. 4( a) to 4(c) are cross-sectional viewsillustrating the procedures to be carried out by the manufacture methodin accordance with this embodiment. FIGS. 5( a), 5(c), 5(e), 6(a), 6(c),and 6(e) are cross-sectional views illustrating procedures to be carriedout by the method for manufacturing the field effect transistor inaccordance with this embodiment. FIGS. 5( b), 5(d), 5(f), 6(b), 6(d),and 6(f) are plan views. FIGS. 5( a), 5(c), 5(e), 6(a), 6(c), and 6(e)are cross-sectional views, taken along each line A-A of FIGS. 5( b),5(d), 5(f), 6(b), 6(d), and 6(f).

The manufacture method in accordance with this embodiment is a methodfor manufacturing a nanowire MOSFET having nanowires formed withstrained SiGe.

First, as shown in FIG. 4( a), a SOI substrate 4 having a supportingsubstrate 1, a buried oxide film 2, and a 20-nm thick SOI layer 3 havinga (001) plane as the principal surface is prepared. A 30-nm thickSi_(0.9)Ge_(0.1) film 20 and a 5-nm thick Si film 21 are formed throughepitaxial growth in this order on the SOI substrate 4. The Si film 21functions as a cap film to prevent the Ge in the Si_(0.9)Ge_(0.1) film20 from becoming volatile GeO and evaporating. The Si film 21 may not beprovided.

Thermal oxidization is then performed at 1150° C. As a result, a 30-nmthick Si_(0.9)Ge_(0.1) film 22 is formed on the buried oxide film 2 dueto the Ge-condensation and interdiffusion between Si and Ge, and asilicon oxide film 23 is formed on the Si_(0.9)Ge_(0.1) film 22, asshown in FIG. 4( b).

The silicon oxide film 23 is then removed with diluted hydrofluoricacid, and a 5-nm thick silicon oxide film 5 and a 20-nm thick siliconnitride film 6 are deposited by CVD in this order, as shown in FIG. 4(c). Here, the silicon oxide film 5 may be formed through thermaloxidization.

A hard mask 9 formed with the silicon oxide film 5 and the siliconnitride film 6 is formed on source and drain portions 7 and a portion 8by a lithography technique using an electron beam or an excimer laserand reactive ion etching (RIE), as shown in FIGS. 5( a) and 5(b). Theportion 8 is to be a channel region. Here, the channel direction is the<1-10> direction, and the width of the hard mask 9 is 40 nm. With thehard mask 9 being used as a mask, RIE is performed to form theSi_(0.9)Ge_(0.1) film 22 of the source and drain portions 7 and theportion 8 to be the channel region into a mesa shape.

After the native oxide film on each sidewall of the mesa is removed withthe use of diluted hydrofluoric acid, the SOI substrate is subjected to5-minute annealing in a 100%-hydrogen atmosphere with atmosphericpressure at 1000° C. As a result, the sidewalls of the mesa arethermally etched with hydrogen, and flat (110) and (−1-10) planes thatare perpendicular to the principal surface of the substrate 4 appears oneach sidewall of the channel portion (the fin portion) 10A of the mesa,as shown in FIGS. 5( c) and 5(d). This is the effect of etching of thesidewalls (thermal etching with hydrogen) that is caused as hydrogenatedsilicon and hydrogenated germanium are generated from a reaction betweenhydrogen and Si and Ge, and the hydrogenated silicon and germaniumvaporize. Since the etching rate of the {110} planes is lower than thoseof the other high-index planes, the (110) plane appears on eachsidewall. The etching effect is in a competitive relationship with thesurface migration of Si and Ge. To make the etching effect dominant, itis preferable that the temperature is increased to 950° C. or higher,and the hydrogen partial pressure is to 0.2×10⁵ Pa or higher. Further,to maintain the mesa structure, particularly, to maintain the finstructure having a high aspect ratio at the channel portion, it ispreferable that the hard mask 9 is formed on the upper face. If one ofthose requirements is not satisfied, the appearance of the (110) planeis not observed. After the thermal etching with hydrogen, the width ofthe fin 10A becomes 20 nm. Eaves 9 a are formed at the lower portion ofthe hard mask 9, as shown in FIG. 5( c) after the hydrogen thermaletching of the sidewalls.

Etching with hot phosphoric acid and diluted hydrofluoric acid is thenperformed to remove the hard mask 9. After that, a silicon oxide filmand a silicon nitride film are again deposited in this order on theentire surface, and patterning is performed on the insulating layerformed with the silicon oxide film and the silicon nitride film by aphoto-lithography and etching techniques. In this manner, the source anddrain portions 7 are covered with the insulating layer 24, and the fin10A to be the channel portion is exposed (see FIGS. 5( e) and 5(f)).

Next, as shown in FIGS. 6( a) and 6(b), the channel portion is thermallyoxidized at 950° C., so as to form a Si_(0.25)Ge_(0.75) wire channel 16of 10 nm in diameter through the Ge-condensation mechanism. At thispoint, the wire channel 16 is coated with a thermal oxide film 25.

After the silicon nitride film 24 is removed with hot phosphoric acid,the thermal oxide film 25 around the wire channel 16 is removed byetching, so as to expose the wire channel 16, as shown in FIGS. 6( c)and 6(d).

A gate oxide film 12 made of HfO₂ is then formed to cover thesurrounding area of the wire channel 16, and a polysilicon film isdeposited on the front face of the substrate. Patterning is thenperformed on the polysilicon film by a photolithography technique, so asto form a gate electrode 13 (FIGS. 6( e) and 6(f)). After that, the sameprocedures as those of the first embodiment are carried out to completea field effect transistor.

The manufacture method in accordance with this embodiment can be used toproduce p-channel MOSFET, as the channel is formed with compressivelystrained SiGe having high hole mobility. In this manner, the drivingcurrent can be increased.

The manufacture method can also be used to produce a CMOSFET circuitconsisting of many p-channel and n-channel Fin FETs.

The manufacture method in accordance with this embodiment can be used toproduce a field effect transistor having a channel patterned in one ofthe [100] directions on a (001) substrate. In such a case, flat {010}plane appear on each sidewall of the fin.

The manufacture method can also be used to produce a field effecttransistor having a channel in the <−110> direction on a (110)substrate. In such a case, flat {001} planes appear on each sidewall ofthe fin.

The manufacture method can also be used to produce a field effecttransistor having a channel patterned in the <−112> direction on a (110)substrate. In such a case, flat {1-11} planes appear on each sidewall ofthe fin.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <001>direction on a (110) substrate. In such a case, flat {110} planes appearon each sidewall of the fin.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <−211>direction on a (111) substrate. In such a case, a flat {0-11} planesappear on each sidewall of the fin.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

Third Embodiment

Referring now to FIGS. 7( a) to 7(f), a method for manufacturing a fieldeffect transistor in accordance with a third embodiment of the presentinvention is described. FIGS. 7( a), 7(c), and 7(e) are cross-sectionalviews illustrating procedures to be carried out by the method formanufacturing the field effect transistor in accordance with thisembodiment. FIGS. 7( b), 7(d), and 7(f) are plan views. FIGS. 7( a),7(c), and 7(e) are cross-sectional views, taken along each line A-A ofFIGS. 7( b), 7(d), and 7(f).

The manufacture method in accordance with this embodiment is anothermethod for manufacturing a nanowire MOSFET having nanowires formed withstrained SiGe.

First, a SOI substrate 4 having a supporting substrate 1, a buried oxidefilm 2, and a 30-nm thick SOI layer 3 having a (001) plane as theprincipal surface is prepared. The same procedures as those of the firstembodiment illustrated in FIGS. 1( d) and 1(e) are then carried out.More specifically, the same procedures as those procedures forperforming thermal etching with hydrogen are carried out so as to formthe fin 10 having the (110) plane 10 a on each sidewall of the mesastructure and the eaves 9 a in the hard mask 9. The (110) plane 10 a isperpendicular to the principal surface of the substrate.

Next, as shown in FIGS. 7( a) and 7(b), a 10-nm thick Si_(0.9)Ge_(0.1)film 26 is formed through epitaxial growth on each sidewall of the fin10. Etching with hot phosphoric acid and diluted hydrofluoric acid isthen performed to remove the hard mask 9. After that, a silicon oxidefilm and a silicon nitride film are again deposited in this order on theentire surface, and patterning is performed on the insulating layer 24formed with the silicon oxide film and the silicon nitride film by alithography technique and RIE. In this manner, the source and drainportions 7 are covered with the insulating layer 24, and the channelportion is exposed (see FIGS. 7( c) and 7(d)).

Next, as shown in FIGS. 7( e) and 7(f), the channel portion is thermallyoxidized at 950° C., so as to form a Si_(0.25)Ge_(0.75) wire channel 16of 10 nm in diameter through the Ge-condensation and the interdiffusionbetween Si and Ge. At this point, the wire channel 16 is coated with athermal oxide film 25.

The same procedures as those of the second embodiment illustrated inFIGS. 6( c) and 6(d) are then carried out. More specifically, after thesilicon nitride film 24 is removed with hot phosphoric acid, the thermaloxide film 25 around the wire channel 16 is removed by etching, so as toexpose the wire channel 16. The same procedures as those of the secondembodiment are carried out thereafter, so as to complete a field effecttransistor.

The manufacture method in accordance with this embodiment can be used toproduce p-channel MOSFET, as the channel is formed with compressivelystrained SiGe having high hole mobility. In this manner, the drivingcurrent can be increased.

The manufacture method can also be used to produce a CMOSFET circuitconsisting of many p-channel and n-channel Fin FETs.

The manufacture method in accordance with this embodiment can be used toproduce p-channel MOSFET, as the channel is formed with compressivelystrained SiGe having high hole mobility. In this manner, the drivingcurrent can be increased.

The manufacture method in accordance with this embodiment can be used toproduce a field effect transistor having a channel patterned in one ofthe [100] directions on a (001) substrate. In such a case, flat {010}plane appear on each sidewall of the fin.

The manufacture method can also be used to produce a field effecttransistor having a channel in the <−110> direction on a (110)substrate. In such a case, flat {001} planes appear on each sidewall ofthe fin.

The manufacture method can also be used to produce a field effecttransistor having a channel patterned in the <−112> direction on a (110)substrate. In such a case, flat {1-11} planes appear on each sidewall ofthe fin.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <001>direction on a (110) substrate. In such a case, flat {110} planes appearon each sidewall of the fin.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <−211>direction on a (111) substrate. In such a case, a flat {0-11} planesappear on each sidewall of the fin.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

Fourth Embodiment

Referring now to FIGS. 8( a) to 9(f), a method for manufacturing a fieldeffect transistor in accordance with a fourth embodiment of the presentinvention is described. FIGS.

8(a), 8(b), 8(d), 9(a), 9(c), and 9(e) are cross-sectional viewsillustrating procedures to be carried out by the method formanufacturing the field effect transistor in accordance with thisembodiment. FIGS. 8( c), 8(e), 9(b), 9(d), and 9(f) are plan views.FIGS. 8( b), 8(d), 9(a), 9(c), and 9(e) are cross-sectional views, takenalong each line A-A of FIGS. 8( c), 8(e), 9(b), 9(d), and 9(f).

This embodiment relates to a method for manufacturing a multiwireMOSFET.

First, as shown in FIG. 8( a), a SOI substrate 4 having a supportingsubstrate 1, a buried oxide film 2, and a 12-nm thick SOI layer 3 havinga (001) plane as the principal surface is prepared. Two sets of a 10-nmthick Si_(0.7)Ge_(0.3) film 41 and a 12-nm thick Si film 42 arealternately formed through epitaxial growth on the SOI layer 3. Another10-nm thick Si_(0.7)Ge_(0.3) film 41 is formed through epitaxial growthat the uppermost portion. After that, a 5-nm thick silicon oxide film 5and a 20-nm thick silicon nitride film 6 are deposited in this order.

Next, as shown in FIGS. 8( b) and 8(c), a mesa structure having a hardmask 9 formed with the silicon oxide film 5 and the silicon nitride film6 at the top is produced in the same manner as in the first embodiment.Here, the channel direction is the <1-10> direction, and the width ofthe hard mask 9 is 32 nm.

After the native oxide film on each sidewall of the mesa is removed withthe use of diluted hydrofluoric acid, the SOI substrate is subjected to5-minute annealing in a 100%-hydrogen atmosphere with atmosphericpressure at 1000° C. As a result, the sidewalls of the mesa structureare thermally etched with hydrogen, and flat {110} planes that areperpendicular to the principal surface of the substrate appear on eachsidewall of the fin 10B to be the channel, as shown in FIGS. 8( d) and8(e). In this embodiment, the fin 10B has a stacked structure formedwith the SOI layer 3, a Si_(0.7)Ge_(0.3) film 41, a Si film 42, anotherSi_(0.7)Ge_(0.3) film 41, another Si film 42, and yet anotherSi_(0.7)Ge_(0.3) film 41. After the thermal etching with hydrogen, thewidth of the fin 10B becomes 12 nm. After the hydrogen thermal etchingof the sidewalls, eaves 9 a are formed at the lower portion of the hardmask 9, as shown in FIG. 8( d).

Etching with hot phosphoric acid and diluted hydrofluoric acid is thenperformed to remove the hard mask 9. After that, an insulating layerformed with a silicon oxide film and a silicon nitride film is againdeposited on the entire surface, and patterning is performed on theinsulating layer by a photolithography and etching technique. In thismanner, the source and drain portions 7 are covered with the insulatinglayer 24, and the fin 10B to be the channel portion is exposed. Chemicaldry etching (CDE) with the use of CF₄ or SF₆ is then performed toselectively remove the Si_(0.7)Ge_(0.3) films 41, and wire channels 43formed with three Si wires are formed (see FIGS. 9( a) and 9(b)). In theselective etching procedure, wet etching with the use of an etchingsolution containing a mixed acid of hydrofluoric acid and nitric acidmay be performed, instead of CDE.

As shown in FIGS. 9( c) and 9(d), to round the corners of the wirechannels 43 made of Si, a thermal oxide film 11 to cover the surroundingarea of the wire channels 43 and the surfaces of the source and drainportions 7 is formed through 30-second RTO at 1050° C. After that, thethermal oxide film 11 is removed with diluted hydrofluoric acid, and thelowermost Si wire of the wire channels 43 is put into a floating statewith respect to the buried oxide film 2. As a result, the width andheight of the wire channels 43 formed with three Si wires become 10 nm.

A gate oxide film 12 made of HfO₂ is then formed to cover thesurrounding area of the three wire channels 43, and a polysilicon filmis further deposited on the entire surface (FIG. 9( e)). The polysiliconfilm is patterned by a photolithography technique, so as to form a gateelectrode 13. The same procedures as those of the first embodiment arecarried out thereafter, so as to complete a field effect transistor.

The manufacture method can also be used to produce a CMOSFET circuitconsisting of many p-channel and n-channel Fin FETs.

The manufacture method in accordance with this embodiment can be used toproduce a field effect transistor having a channel patterned in one ofthe [100] directions on a (001) substrate. The manufacture method inaccordance with this embodiment is particularly effective in producingan n-channel MOSFET to achieve greater driving current, as a flat {010}planes appear on each sidewall, the top and the bottom surface of thewire.

The manufacture method can also be used to produce a field effecttransistor having a channel in the <−110> direction on a (110)substrate. In such a case, the manufacture method is effective inproducing both n-channel and p-channel MOSFETs to achieve greaterdriving current, as flat {001} planes appear on each sidewall of thewire and flat {110} planes appear on the top and bottom of the wire.

The manufacture method can also be used to produce a field effecttransistor having a channel patterned in the <−112> direction on a (110)substrate. In such a case, flat {1-11} planes appear on each sidewall ofthe wire, and therefore, the same driving current can be achieved inboth a p-channel MOSFET and an n-channel MOSFET. Thus, the circuitdesign becomes simpler.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <001>direction on a (110) substrate. In such a case, the manufacture methodis particularly effective in producing a p-channel MOSFET to achievegreater driving current, as flat {−110} planes appear on each sidewallof the wire.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <−211>direction on a (111) substrate. In such a case, the manufacture methodis particularly effective in producing a p-channel MOSFET to achievegreater driving current, as flat (0-11) planes appear on each sidewallof the wire.

In this embodiment, if a SOI substrate including a SOI layer that is asilicon layer having tensile strain in the plane (a strained SOIsubstrate) is used, a multiwire MOSFET having tensile strain in thechannel direction is formed through the same procedures as above. Insuch a case, the electron mobility becomes high by virtue of theuniaxial stain in the channel direction, and the ON current of ann-channel MOSFET becomes higher.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

In this embodiment, the Ge composition of the Si_(1-x)Ge_(x) films 41 tobe removed is 0.3. If the composition is 0.25 or greater, the etchingrate of SiGe rapidly increases. Therefore, it is preferable that the Gecomposition x of the Si_(1-x)Ge_(x) films 41 is in the range of 0.25 to0.6. The upper limit value is determined by the following reasons. In acase where a Si_(1-x)Ge_(x) film is grown on a Si substrate, the latticemismatch between the Si and the SiGe film becomes larger as thecomposition x is greater, and large compressive strain is caused in theSiGe film. Where the SiGe film thickness is 10 nm as in this embodiment,if the composition x is larger than 0.6, the stain in the SiGe filmexceeds a critical value, and a lattice defect is formed during theepitaxial growth.

Fifth Embodiment

Referring now to FIGS. 10( a) to 11(f), a method for manufacturing afield effect transistor in accordance with a fifth embodiment of thepresent invention is described. FIGS. 10( a), 10(b), 10(d), 11(a),11(c), and 11(e) are cross-sectional views illustrating procedures to becarried out by the method for manufacturing the field effect transistorin accordance with this embodiment. FIGS. 10( c), 10(e), 11(b), 11(d),and 11(f) are plan views. FIGS. 10( b), 10(d), 11(a), 11(c), and 11(e)are cross-sectional views, taken along each line A-A of FIGS. 10( c),10(e), 11(b), 11(d), and 11(f).

This embodiment relates to a method for manufacturing a multiwire MOSFETthat has multiwires formed with strained SiGe to be the channel. Sincethe strained SiGe has high hole mobility, a higher driving current thanthe driving current obtained in a case where the channel is made of Sican be obtained, especially when the manufacture method in accordancewith this embodiment is used to produce a p-cannel MOSFET.

First, as shown in FIG. 10( a), a SOI substrate 4 having a supportingsubstrate 1, a buried oxide film 2, and a 10-nm thick SOI layer 3 havinga (001) plane as the principal surface is prepared. Three sets of a10-nm thick Si_(0.7)Ge_(0.3) film 41 and a 30-nm thickSi_(0.95)Ge_(0.05) film 44 are alternately formed through epitaxialgrowth on the SOI layer 3. Another 10-nm thick Si_(0.7)Ge_(0.3) film 41is formed through epitaxial growth at the uppermost portion. After that,a 5-nm thick silicon oxide film 5 and a 20-nm thick silicon nitride film6 are deposited in this order.

Next, as shown in FIGS. 10( b) and 10(c), a mesa structure having a hardmask 9 formed with the silicon oxide film 5 and the silicon nitride film6 at the top is produced in the same manner as in the first embodiment.Here, the channel direction is the <1-10> direction, and the width ofthe hard mask 9 is 40 nm.

After the native oxide film on each sidewall of the mesa structure isremoved with the use of diluted hydrofluoric acid, the SOI substrate issubjected to 5-minute annealing in a 100%-hydrogen atmosphere withatmospheric pressure at 1000° C. As a result, the sidewalls of the mesastructure are thermally etched with hydrogen, and flat {110} planes 10Cathat are perpendicular to the principal surface of the substrate appearon each sidewall of the fin 10C to be the channels, as shown in FIGS.10( d) and 10(e). After the thermal etching with hydrogen, the width ofthe fin 10C becomes 20 nm. After the hydrogen thermal etching of thesidewalls, eaves 9 a are formed at the lower portion of the hard mask 9,as shown in FIG. 10( d).

Etching with hot phosphoric acid and diluted hydrofluoric acid is thenperformed to remove the hard mask 9. After that, an insulating layerformed with a silicon oxide film and a silicon nitride film is againdeposited on the entire surface, and patterning is performed on theinsulating layer by a photolithography and an etching techniques. Inthis manner, the source and drain portions 7 are covered with theinsulating layer 24, and the fin 10C to be the channel portion isexposed. Chemical dry etching (CDE) with the use of CF₄ or SF₆ is thenperformed to selectively remove the Si_(0.7)Ge_(0.3) films 41, and wirechannels 45 formed with three Si_(0.95)Ge_(0.05) wires is formed (seeFIGS. 11( a) and 11(b)). In the selective etching procedure, wet etchingwith the use of an etching solution containing a mixed acid ofhydrofluoric acid and nitric acid may be performed, instead of CDE.

As shown in FIGS. 11( c) and 11(d), the fin 10C to be the channel isthermally oxidized at 950° C., so that three wire channels 46 that are10 nm in diameter and are made of Si_(0.62)Ge_(0.38) are formed throughthe Ge-condensation process. At this point, the surrounding area of thethree wire channels 46 is covered with a thermal oxide film 25.

After the silicon nitride film of the insulating layer 24 is removedwith thermal phosphoric acid, etching with diluted hydrofluoric acid isperformed to remove the thermal oxide film 25 covering the surroundingarea of the three wire channels 46, and to expose the surfaces of thethree wire channels 46. A gate oxide film 12 made of HfO₂ is then formedto cover the surrounding area of the three wire channels 46, and apolysilicon film is further deposited on the entire surface. As shown inFIGS. 11( e) and 11(f), the polysilicon film is then patterned by aphotolithography technique, so as to form a gate electrode 13. The sameprocedures as those of the first embodiment are carried out thereafter,so as to complete a field effect transistor.

The manufacture method can also be used to produce a CMOSFET circuitconsisting of many p-channel and n-channel Fin FETs.

The manufacture method in accordance with this embodiment can be used toproduce a field effect transistor having a channel patterned in one ofthe [100] directions on a (001) substrate. In such a case, flat (010)planes appear on each sidewall of the wire.

The manufacture method can also be used to produce a field effecttransistor having a channel in the <−110> direction on a (110)substrate. In such a case, flat (001) planes appear on each sidewall ofthe wire.

The manufacture method can also be used to produce a field effecttransistor having a channel patterned in the <−112> direction on a (110)substrate. In such a case, flat {1-11} planes appear on each sidewall ofthe wire.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <001>direction on a (110) substrate. In such a case, flat {−110} planesappear on each sidewall of the wire.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <−211>direction on a (111) substrate. In such a case, flat {0-11} planesappear on each sidewall of the wire.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

In this embodiment, it is also preferable that the Ge composition x ofthe Si_(1-x)Ge_(x) films 41 to be removed is in the range of 0.25 to0.6, as in the fourth embodiment. Meanwhile, it is preferable that theGe composition x of the Si_(1-x)Ge_(x) films 44 to remain is less than0.25, and, more preferably, 0.1 or less.

Sixth Embodiment

Referring now to FIGS. 12( a) to 13(d), a method for manufacturing afield effect transistor in accordance with a sixth embodiment of thepresent invention is described. FIGS. 12( a), 12(c), 12(e), 13(a), and13(c) are cross-sectional views illustrating procedures to be carriedout by the method for manufacturing the field effect transistor inaccordance with this embodiment. FIGS. 12( b), 12(d), 12(f), 13(b), and13(d) are plan views. FIGS. 12( a), 12(c), 12(e), 13(a), and 13(c) arecross-sectional views, taken along each line A-A of FIGS. 12( b), 12(d),12(f), 13(b), and 13(d).

First, a 20-nm thick silicon nitride film is deposited on a siliconsubstrate 60 having a (001) plane as the principal surface. Patterningis performed on the silicon nitride film by a lithography techniqueusing an electron beam or an excimer laser and a reactive ion etching(RIE), and a hard mask 6 is formed on source and drain portions 7 and aportion 8 to be the channel region. Here, the channel direction is the<1-10> direction, and the width of the hard mask 6 is 40 nm. With thehard mask 6 being used as a mask, RIE is performed to form the sourceand drain portions 7 and the channel region 8 into a mesa shape (FIGS.12( a) and 12(b)).

After the native oxide film on each sidewall of the mesa structure isremoved with the use of diluted hydrofluoric acid, the silicon substrate60 is subjected to 5-minute annealing in a 100%-hydrogen atmosphere withatmospheric pressure at 950° C. As a result, the sidewalls of the mesastructure 10 are thermally etched, and flat {110} planes 10 a that areperpendicular to the principal surface of the substrate appear on eachsidewall of the fin 10 to be the channel portion 8, as shown in FIGS.12( c) and 12(d).

Further, {111} planes appear on a connecting portion 61 that is locatedat the lower portion of the mesa structure and between the fin 10 andthe substrate 60. The {111} planes crosse the {110} planes 10 a at theupper portion of the mesa. This is the effect of etching of thesidewalls of the fin 10 and the surface of the substrate 60 (thermaletching with hydrogen) that is caused as hydrogenated silicon isgenerated from a reaction between hydrogen and Si, and the hydrogenatedsilicon vaporizes. Since the etching rates of the {110} planes and the{111} planes are lower than those of the other high-index planes, the{110} planes and the {111} planes appear. After the thermal etching withhydrogen, the width of the fin 10 becomes 15 nm. Here, the position ofthe lower end of the fin 10 is represented by two straight lines definedby the intersection lines between the (111) plane and the (110) planeand between the (−1-11) plane and the (−1-10) plane. Accordingly, thefin 10 having a very small variation in width is formed. After theydrogen etching of the sidewalls, eaves 6 a are formed at the lowerportion of the hard mask 6, as shown in FIG. 12( c).

After the fin 10 is filled with an interlayer insulating film 62,flattening is performed by CMP (Chemical Mechanical Polishing) until thetop portion of the hard mask 6 is exposed, as shown in FIGS. 12( e) and12(f).

Etchback is then performed on the interlayer insulating film 62 by RIE,and the {110} planes as the sidewalls of the fin 10 are again exposedwith the use of diluted hydrofluoric acid, as shown in FIGS. 13( a) and13(b). After that, the eaves 6 a of the hard mask 6 are removed. At thispoint, the silicon nitride film 6 is not completely removed, but ispartially left on the mesa structure.

A gate oxide film 12 made of HfO₂ is then formed on the sidewalls of thefin 10, and a polysilicon film is deposited. Patterning is thenperformed on the polysilicon film by a photolithography technique, so asto form a gate electrode 13 (FIGS. 13( c) and 13(d)). After that, thesame procedures as those of the first embodiment are carried out tocomplete a field effect transistor.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

In a field effect transistor manufactured by the manufacture method inaccordance with this embodiment, the width of the bottom portion of thefin having the {110} planes as each sidewall are uniquely defined by theintersection lines between the {111} planes and the {110} planes.Accordingly, the variations in width along fins are restricted to avalue equivalent to several atoms or less.

The manufacture method can also be used to produce a CMOSFET circuitconsisting of many p-channel and n-channel Fin FETs.

Seventh Embodiment

Referring now to FIGS. 14( a) to 18(b), a method for manufacturing acomplementary MOSFET (CMOSFET) in accordance with a seventh embodimentof the present invention is described. This embodiment relates to amethod for manufacturing a CMOSFET that includes an n-channel Fin FEThaving the channel formed with a SOI layer, and a p-channel Fin FEThaving the channel formed with a strained SGOI layer. Here, a SGOIsubstrate is a substrate that has the same structure as a SOI substrate,except that the SOI layer is replaced with a SiGe layer. FIGS. 14( a),14(c), 15(a), 15(c), 16(a), 16(c), 17(a), 17(c), and 18(a) arecross-sectional views illustrating procedures to be carried out by themethod for manufacturing the field effect transistor in accordance withthis embodiment. FIGS. 14( b), 14(d), 15(b), 15(d), 16(b), 16(d), 17(b),17(d), and 18(b) are plan views. FIGS. 14( a), 14(c), 15(a), 15(c),16(a), 16(c), 17(a), 17(c), and 18(a) are cross-sectional views, takenalong each line A-A of FIGS. 14( b), 14(d), 15(b), 15(d), 16(b), 16(d),17(b), 17(d), and 18(b).

First, a SOI substrate 4 having a supporting substrate 1, a buried oxidefilm 2, and a SOI layer 3 having a (001) plane as the principal surfaceis prepared. The same procedures as those of the first embodiment arethen carried out to form a SOI mesa structure in each of an n-channeltransistor formation region 80 and a p-channel transistor formationregion 90, as shown in FIGS. 14( a) and 14(b). The same procedures asthose of the first embodiment are still carried out to perform thermaletching with hydrogen on the sidewalls of the mesa structures, as shownin FIGS. 14( c) and 14(d). As a result, a fin 10 having a flat surface10 a on each sidewall of each mesa structure is formed. The flat surface10 a is perpendicular to the substrate. At this point, eaves 9 a areformed at the lower portion of each hard mask 9.

The same procedures as those of the first embodiment are carried out toremove the eaves 9 a of the hard mask 9, and an n-channel mesa 81 and ap-channel mesa 91 are formed, as shown in FIGS. 15( a) and 15(b). Afterthe hard mask 9 is removed by etching, a thermal oxide film 11 to coverthe surfaces of the mesa structures is formed by 30-second rapid thermaloxidization (RTO) at 1050° C., and a 20-nm thick silicon nitride film 83is further formed by CVD on the entire surface, as shown in FIGS. 15( c)and 15(d).

Next, as shown in FIGS. 16( a) and 16(b), the silicon nitride film 83 onthe p-channel transistor formation region 90 is removed by wet etchingwith thermal phosphoric acid, and the thermal oxide film 11 on eachsidewall of the p-channel fin 10 is removed by etching with dilutedhydrofluoric acid, so as to expose the surfaces of the fins 10. At thispoint, a silicon nitride film 83 a is left on the p-channel mesa 91. Asshown in FIGS. 16( c) and 16(d), a 10-nm thick Si_(0.85)Ge_(0.15) film26 is formed through epitaxial growth on each sidewall of the p-channelmesa 91.

Next, as shown in FIGS. 17( a) and 17(b), the sidewalls of the p-channelmesa 91 are thermally oxidized until the width of the mesa 91 becomes 10nm. As a result, a mesa structure 92 made of Si_(0.7)Ge_(0.3) is formedthrough the Ge-condensation process. At this point, the surrounding areaof the mesa structure 92 is covered with a thermal oxide film 84. Asshown in FIGS. 17( c) and 17(d), the silicon nitride films 83 and 83 aare removed with hot phosphoric acid, and the silicon oxide film 11 andthe thermal oxide film 84 are removed with diluted hydrofluoric acid. Asa result, a mesa structure 81 having a fin made of silicon appears onthe n-channel transistor formation region, and the mesa structure 92having a fin 10A made of Si_(0.7)Ge_(0.3) appears on the p-channeltransistor formation region.

Next, as shown in FIGS. 18( a) and 18(b), a gate oxide film 12 made ofHfO₂ is deposited on the entire surface, and a polysilicon film isfurther deposited on the entire surface. Patterning is then performed onthe polysilicon film by a photolithography technique, so as to form gateelectrodes 13. After that, the same procedures as those of the firstembodiment are carried out to complete a CMOSFET.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

In this embodiment that involves a substrate having a (001) plane as theprincipal surface, the direction of the fin to be the channel of ann-channel MOSFET is the same as the direction of the fin to be thechannel of a p-channel MOSFET. However, the directions of the two finsmay differ from each other by 45 degrees or 90 degrees. In a case wherethe principal surface of the substrate is a (110) plane and one of thechannels extends in the [−110] direction, the directions of the two finsmay differ from each other by 90 degrees. This also applies to thefollowing eighth to tenth embodiments.

Eighth Embodiment

Referring now to FIGS. 19( a) to 23(b), a method for manufacturing aCMOSFET in accordance with an eighth embodiment of the present inventionis described. The CMOSFET to be manufactured by the manufacture methodin accordance with this embodiment includes an n-channel Fin FET havingthe channel formed with a SOI layer, and a p-channel Fin FET having thechannel formed with a strained SGOI layer. The manufacture method inaccordance with this embodiment differs from the manufacture method inaccordance with the seventh embodiment. FIGS. 19( a) to 20(c) arecross-sectional views illustrating procedures to be carried out by themanufacture method in accordance with this embodiment. FIGS. 21( a),21(c), 22(a), 22(c), and 23(a) are cross-sectional views illustratingmanufacturing procedures. FIGS. 21( b), 21(d), 22(b), 22(d), and 23(b)are plan views. FIGS. 21( a), 21(c), 22(a), 22(c), and 23(a) arecross-sectional views, taken along each line A-A of FIGS. 21( b), 21(d),22(b), 22(d), and 23(b).

First, as shown in FIG. 19( a), a SOI substrate 4 having a supportingsubstrate 1, a buried oxide film 2, and a 50-nm thick SOI layer 3 isprepared. A device isolation region 72 is then formed on the SOI layer 3by the known shallow trench isolation (STI) process. An n-channeltransistor formation region 80 and a p-channel transistor formationregion 90 are isolated from each other by the device isolation region72.

As shown in FIG. 19( b), a 5-nm thick thermal oxide film 73 and a 20-nmthick silicon nitride film 74 are formed on the 50-nm thick SOI layer 3,and the portion of the silicon nitride film 74 located on the p-channeltransistor formation region 90 is removed by a photolithographytechnique and RIE.

As shown in FIG. 19( c), the portion of the thermal oxide film 73located on the p-channel transistor formation region 90 is then removedby etching with diluted hydrofluoric acid. After that, a 50-nm thickSi_(0.85)Ge_(0.15) film 75 and a 10-nm thick Si film 76 are formed onthe p-channel transistor formation region 90 through epitaxial growth inthis order.

As shown in FIG. 20( a), the p-channel transistor formation region 90 issubjected to thermal oxidization, and an oxide film 77 is formed.Further, a 50-nm thick SiGe film 75 a is formed through theGe-condensation process.

As shown in FIG. 20( b), the thermal oxide films 77 and 73 and thesilicon nitride film 74 are removed with diluted hydrofluoric acid andthermal phosphoric acid, so as to expose the surface of the SOI layer 3in the n-channel transistor formation region 80 and the surface of theSiGe film 75 a in the p-channel transistor formation region 90.

As shown in FIG. 20( c), a 2-nm thick thermal oxide film 78 and a 20-nmthick silicon nitride film 79 are again formed on the respectivesurfaces of the n-channel transistor formation region 80 and thep-channel transistor formation region 90.

Patterning is then performed on the silicon nitride film 79 and thethermal oxide film 78, so as to form hard masks 9 formed with thethermal oxide film 78 and the silicon nitride film 79 on the n-channeltransistor formation region 80 and the p-channel transistor formationregion 90, respectively. With the hard masks 9 being used, RIE isperformed to form the source and drain portions and the channel region 8into mesa shapes, as shown in FIGS. 21( a) and 21(b).

The thermal etching with the use of hydrogen described in the firstembodiment is then performed, so as to form mesa structures that includea fin 10 and a fin 10A on the n-channel transistor formation region 80and the p-channel transistor formation region 90, respectively. The fin10 and the fin 10A have flat sidewalls that are perpendicular to thesubstrate (FIGS. 21(c) and 21(d)). At this point, eaves 9 a are formedin the hard masks 9.

The same procedures as those of the first embodiment are then carriedout to remove the eaves 9 a of the hard masks 9 (FIGS. 22( a) and22(b)). A thermal oxide film 11 is then formed on each sidewall of thefin 10 and the fin 10A, and the edge portions of the fins 10 and 10A arerounded. Further, the widths of the fins 10 and 10A are adjusted toappropriate values (FIGS. 22( c) and 22(d)).

The thermal oxide films 11 are then removed to expose the sidewalls ofthe fins 10 and 10A in the same manner as in the first embodiment. Afterthat, a gate oxide film 12 is formed on each of the exposed sidewalls,and a polysilicon film is further deposited on the entire surface. Inthe same manner as in the first embodiment, the polysilicon film is thenpatterned by a photolithography technique and RIE, so as to form gateelectrodes 13 (FIGS. 23( a) and 23(b)). The same procedures as those ofthe first embodiment are carried out thereafter, so as to complete aCMOSFET.

The manufacture method in accordance with this embodiment can be used toproduce a field effect transistor having a fin-like channel patterned inone of the [110] directions on a (001) substrate. The manufacture methodin accordance with this embodiment is particularly effective inproducing a p-channel MOSFET to achieve greater driving current, as thesidewalls of the fin are formed with {110} planes having higher holemobility than on the {100} planes.

Other than that, the manufacture method in accordance with thisembodiment can be used to produce a field effect transistor having achannel patterned in one of the [100] directions on a (001) substrate.In such a case, the manufacture method is particularly effective inproducing an n-channel MOSFET to achieve greater driving current, asflat {010} planes appear on each sidewall of the fin. The manufacturemethod can also be used to produce a field effect transistor having achannel in the <−110> direction on a (110) substrate. In such a case,the manufacture method is particularly effective in producing ann-channel MOSFET to achieve greater driving current, as flat {001} planeappears on each sidewall of the fin.

The manufacture method can also be used to produce a field effecttransistor having a channel patterned in the <−112> direction on a (110)substrate. In such a case, flat {111} planes appears on each sidewall ofthe fin, and therefore, the same driving current can be achieved in botha p-channel MOSFET and an n-channel MOSFET. Thus, the circuit designbecomes simpler.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the <001>direction on a (110) substrate. In such a case, the manufacture methodis particularly effective in producing a p-channel MOSFET to achievegreater driving current, as flat {110} planes appear on each sidewall ofthe fin.

The manufacture method in accordance with this embodiment can also beused to produce a field effect transistor having a channel in the [−211]direction on a (111) substrate.

In such a case, the manufacture method is particularly effective inproducing a p-channel MOSFET to achieve greater driving current, as flat{011} planes appear on each sidewall of the fin.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained.

As a modification of this embodiment, a SOI substrate (strained SOIsubstrate) that includes a silicon layer as a SOI layer having tensilestrain c in the plane may be used, and the same procedures as those ofthis embodiment are then carried out to form a CMOSFET. In this CMOSFET,the channel of the n-channel MOSFET is formed with strained Si havingtensile strain in the channel direction, and the channel of thep-channel MOSFET is formed with strained Si_(1-x)Ge_(x) havingcompressive strain in the channel direction. However, to maintain thecompressive strain of the p-channel, ε/ε₀<x should be satisfied. Here,ε₀ is the strain caused by the lattice mismatch between Si and Ge, andis 0.042. The inequation means that the lattice constant of thelattice-relaxed Si_(1-x)Ge_(x) becomes larger than the in-plane latticeconstant of the original strained SOI substrate.

Ninth Embodiment

Referring now to FIGS. 24( a) to 27(b), a method for manufacturing aCMOSFET in accordance with a ninth embodiment of the present inventionis described. This embodiment relates to a method for manufacturing aCMOSFET that includes an n-channel Fin FET having the channel formedwith a Si layer, and a p-channel Fin FET having the channel formed witha strained SiGe layer. In this CMOSFET, the n-channel Fin FET and thep-channel Fin FET are formed on a bulk Si substrate. FIGS. 24( a) to24(c) are cross-sectional views illustrating procedures to be carriedout by the manufacture method in accordance with this embodiment. FIGS.25( a), 25(c), 26(a), 26(c), and 27(a) are cross-sectional viewsillustrating manufacturing procedures. FIGS. 25( b), 25(d), 26(b),26(d), and 27(b) are plan views. FIGS. 25( a), 25(c), 26(a), 26(c), and27(a) are cross-sectional views, taken along each line A-A of FIGS. 25(b), 25(d), 26(b), 26(d), and 27(b).

First, as shown in FIG. 24( a), a 20-nm thick thermal oxide film 100 isformed on a bulk Si substrate 60 having the (001) plan as the principalsurface. After that, a photoresist is applied onto the thermal oxidefilm 100, and a resist pattern 102 is left on an n-channel transistorformation region 80 by a photolithography technique. With the resistpattern 102 serving as a mask, RIE is performed to remove the thermaloxide film 100 on a p-channel transistor formation region 90, and form a60-nm deep groove 104 in the Si substrate 60.

Next, as shown in FIG. 24( b), the resist pattern 102 is removed, and aSi_(0.7)Ge_(0.3) film 106 is formed through epitaxial growth in thegroove 104, so that the surface of the p-channel transistor formationregion 90 is in the same plane as the Si surface of the n-channeltransistor formation region 80. After the thermal oxide film 100 on then-channel transistor formation region 80 is removed, a 2-nm thickthermal oxide film 108 is formed on the entire surface, and a 20-nmthick silicon nitride film 110 is deposited on the entire surface, asshown in FIG. 24( c).

Patterning is then performed on the silicon nitride film 110 and thethermal oxide film 108 by a lithography technique and RIE using anelectron beam or an excimer laser. As a result, as shown in FIGS. 25( a)and 25(b), hard masks 9 formed with the thermal oxide film 108 and thesilicon nitride film 110 are formed at the source and drain portions 7and the portion 8 to be the channel region on the n-channel transistorformation region 80 and the p-channel transistor formation region 90,respectively. Here, the channel direction is the <1-10> direction, andthe width of each of the hard masks 9 is 40 nm. With the hard masks 9being used, RIE is performed to form the source and drain portions 7 andthe portion 8 to be the channel region into mesa shapes.

The same procedures as those of the sixth embodiment illustrated inFIGS. 12( c) and 12(d) are then carried out, so as to form mesastructures that include a fin 10 and a fin 10A on the n-channeltransistor formation region 80 and the p-channel transistor formationregion 90, respectively. The fin 10 and the fin 10A have flat {110}planes as sidewalls that are perpendicular to the principal surface ofthe substrate (FIGS. 25( c) and 25(d)). At this point, {111} planesappear at the connecting portions between the fins and the substrate atthe bottom portions of the mesa structures. The {111} planes cross the{110} planes of the sidewalls of the fins.

Next, as shown in FIGS. 26( a) and 26(b), an interlayer insulating film62 is deposited on the entire surface, and flattening is performed onthe interlayer insulating film 62 by CMP until the upper faces of thehard masks 9 are exposed. As shown in FIGS. 26( c) and 26(d), theinterlayer insulating film 62 is further etched to expose the sidewallsof the fins 10 and 10A, and the eaves 9 a (see FIG. 26( a)) of the hardmasks 9 are removed.

The same procedures as those of the sixth embodiment are then carriedout to form a gate oxide film 12 on each of the channel regions of thefins 10 and 10A, and form gate electrodes 13 to cover the gate oxidefilms 12, as shown in FIGS. 27( a) and 27(b). After that, the sameprocedures as those of the sixth embodiment are continued, so as to forma CMISFET.

As described above, in accordance with this embodiment, size and shapevariations among channels are made as small as possible, and fieldeffect transistors having the smallest possible channel widths can beobtained, as in the sixth embodiment.

Tenth Embodiment

Referring now to FIGS. 28( a) to 30(b), a method for manufacturing aCMOSFET in accordance with a tenth embodiment of the present inventionis described. This embodiment relates to a method for manufacturing aCMOSFET that includes an n-channel Fin FET having the channel formedwith a Si layer, and a p-channel Fin FET having the channel formed witha strained SiGe layer. In this CMOSFET, the n-channel Fin FET and thep-channel Fin FET are formed on a bulk Si substrate. FIGS. 28( a),28(c), 29(a), 29(c), and 30(a) are cross-sectional views illustratingmanufacturing procedures. FIGS. 28( b), 28(d), 29(b), 29(d), and 30(b)are plan views.

FIGS. 28( a), 28(c), 29(a), 29(c), and 30(a) are cross-sectional views,taken along each line A-A of FIGS. 28( b), 28(d), 29(b), 29(d), and30(b).

First, the same procedures as those of the sixth embodiment are carriedout to form hard masks 6 formed with silicon nitride film on a bulk Sisubstrate 60 having a (001) plane as the principal surface. With thehard masks 6 being used, RIE is performed to form source and drainportions 7 and a portion 8 to be the channel region into mesa shapes onan n-channel transistor formation region 80 and a p-channel transistorformation region 90, respectively.

The same procedures as those of the sixth embodiment illustrated inFIGS. 12( c) and 12(d) are then carried out, so as to form mesastructures that include a fin 10 on each of the n-channel transistorformation region 80 and the p-channel transistor formation region 90.The fins 10 have flat {110} planes as sidewalls that are perpendicularto the principal surface of the substrate (FIGS. 28( c) and 28(d)). Atthis point, {111} planes appear at the connecting portions between thefins and the substrate at the bottom portions of the mesa structures.The {111} planes cross the {110} planes of the sidewalls of the fins 10.

After a silicon oxide film is deposited on the entire surface, thesilicon oxide film on the p-channel transistor formation region 90 isremoved by a photolithography technique and chemical dry etching or wetetching, and a silicon oxide film 120 is left only on the n-channeltransistor formation region 80, as shown in FIGS. 29( a) and 29(b).After that, a 10-nm Si_(0.85)Ge_(0.15) film 122 is formed throughselective epitaxial growth on each sidewall of the fin 10 on thep-channel transistor formation region 90 (FIG. 29( a)).

Next, as shown in FIGS. 29( c) and 29(d) the p-channel transistorformation region 90 is thermally oxidized, and the Ge-condensationprocess are performed until the width of the fin 10A on the p-channeltransistor formation region 90 becomes 10 nm. In this manner, the Gecomposition is increased to 30%. At this point, the side portions of thefin 10A are covered with the silicon oxide film 120.

After the entire surface of the Si substrate is filled with a siliconoxide film 62, flattening is performed by CMP until the upper faces ofthe hard masks 6 are exposed, as shown in FIGS. 30( a) and 30(b). Afterthat, the same procedures as those of the ninth embodiment are carriedout, so as to form a CMOSFET.

In each of the above described first to tenth embodiments, modificationsmay be made to the gate insulating film, the gate electrode, and thesource and drain structure. As for the gate insulating film, it ispossible to use a high permittivity (high-k) dielectric material otherthan HfO₂ mentioned in each embodiment, such as HfSiON, HfSiO₂, HfO₂,HfArO_(x), or ZrO₂. It is also possible to use a stacked structureformed with one of those high-k dielectric materials and an interfacelayer made of SiO₂ or GeO₂. Alternatively, a Si oxynitride film (SiON)may be used. Also, it is of course possible to use a SiO₂ film.

As for the gate electrode, it is possible to use Ni silicide, TiN, Nigermanide (Ni_(1-x)Ge_(x)), Ni germano silicide (NiSi(Ge)), W silicide,TiSiN, TaN, TaSiN, WN, AlN, or the like. Also, it is possible to combinetechniques for reducing the parasitic resistance in the source and drainportions used in conventional CMOS manufacturing processes. For example,a Si layer, a SiGe layer, or a Ge layer can be made thicker throughselective epitaxial growth. Alternatively, the source and drain portionsmay be entirely or partially formed with metal silicides.

The appropriate temperature for performing hydrogen thermal etching isin the range of 950° C. to 1100° C. This is because the etching effectbecomes smaller if the temperature is lower than 950° C., and each findoes not maintain its rectangular shape and is put into a dot-like stateif the temperature becomes higher than 1100° C. To achieve a sufficientetching effect, the hydrogen partial pressure should be 0.2×10⁵ Pa orhigher. The effective etching time, or the total of the time duringwhich the above thermal etching conditions are satisfied in a ramping upand down processes and the time during which etching is performed at afixed temperature, is in the range of one minute to 30 minutes.

At the time of hydrogen annealing, it is possible to add annealing underconditions other than the temperature and pressure for the above thermaletching (for example, annealing at a temperature lower than 950° C. witha hydrogen partial pressure of 1×10⁵ Pa, or annealing at 1000° C. with ahydrogen partial pressure of 0.1×10⁵ Pa). By doing so, the flatteningeffect of surface migration can be achieved as well as the effect ofanisotropic hydrogen thermal etching.

The hydrogen partial pressure in either a ramping up or a ramping downprocesses or in both a ramping up and a ramping down processes may beset at a value smaller than 0.2×10⁵ Pa. By doing so, the etching in aramping up or a ramping down processes can be restricted, and theetching controllability can be increased.

The pre-processing of the hydrogen thermal etching may involve not onlythe processing with diluted hydrofluoric acid but also formation of asilicon oxide film of 1 nm to 5 nm in thickness. The oxide film may beformed through thermal oxidization, or may be formed with ozone water orhydrogen peroxide. In that case, the oxide film vaporizes during aramping up process in a hydrogen annealing furnace, and accordingly, theSi or SiGe surface is not exposed to the atmosphere. Thus, thereproducibility of the thermal etching is increased.

Also, fins or an array of stacked nanowires may be connected to a pairof source and drain regions, and be regarded as a single transistor.Further, the procedures according to any of the first to fifthembodiments may be carried out to form a structure including a bulk Sisubstrate. In that case, the filling procedure involving an interlayerinsulating film and the procedure for removing the interlayer insulatingfilm to expose the top of the fin, as illustrated in FIGS. 12( e) to13(b), are added to the procedures according to any of the first tofifth embodiments.

According to the manufacture method of any embodiment of the presentinvention, a semiconductor film containing Si or Ge is formed on a Sisubstrate or a SOI substrate, and a hard mask of an insulating film isformed at the uppermost portion of the semiconductor film. With the useof the hard mask, the semiconductor film is formed into a mesastructure, and is subjected to a heat treatment in a hydrogen atmosphereof 0.2×10⁵ Pa or higher at a temperature between 950° C. and 1100° C.Through the heat treatment, the sidewalls of the mesa are etched and areflattened, as a low-index plane such as a (110) plane appears on eachsidewall. Accordingly, the width of the mesa is reduced, while thesidewalls of the mesa are flattened. In the manufacture of Fin FETs,line edge roughness and variations in the cross-sectional shape causedby the lithography process are made smaller, and fins of 10 nm or lesshaving uniform widths in width can be produced.

In the formation of a multi-nanowire channel in which nanowires arestacked in a direction perpendicular to the substrate, as in the fourthor fifth embodiment, the widths of the upper portion and the lowerportion of the channel can be made equal to each other by virtue of theappearance of a crystal plane perpendicular to the substrate. As aresult, variations in device characteristics among Fin FETs andmulti-nanowire FETs are reduced, and higher driving current can beachieved.

Each of the embodiments of the present invention can provide fieldeffect transistors and a method for manufacturing the field effecttransistors among which size and shape variations among channels aremade as small as possible, and channels having the smallest possiblechannel widths can be obtained.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcepts as defined by the appended claims and their equivalents.

1.-18. (canceled)
 19. A method for manufacturing a field effecttransistor, comprising: forming a mask comprising an insulating film ona SOI substrate, the SOI substrate having a SI layer formed on aninsulating layer; forming the Si layer into a mesa structure byperforming etching with the use of the mask, the mesa structure having apair of sidewalls extending in a first direction parallel to an upperface of the SOI substrate, the sidewalls facing each other; reducing adistance between the sidewalls to be less than a width of the mask in asecond direction perpendicular to the first direction and flattening thesidewalls by performing a heat treatment in a hydrogen atmosphere, theflattened sidewalls being formed with one of a {110} plane or a {111}plane; forming a gate insulating film covering the flattened sidewalls;forming a gate electrode covering the gate insulating film; and formingsource and drain regions at portions of the mesa structure, the portionsbeing located on two sides of the gate electrode.
 20. The methodaccording to claim 19, further comprising: oxidizing the flattenedsidewalls of the mesa structure to form an oxide film on the flattenedsidewalls and to thin the mesa structure; and removing the oxide film,being carried out before the forming the gate insulating film.
 21. Themethod according to claim 19, further comprising: forming a SiGe film onthe Si layer; performing thermal oxidization to turn a stacked structureof the Si layer and the SiGe film into a stacked structure of a SiGelayer and a silicon oxide layer; and removing the silicon oxide layer toleave the SiGe layer on the insulating layer, being carried out prior tothe forming the mask.
 22. The method according to claim 19, wherein themesa structure having the flattened sidewalls is made of Si, the methodfurther comprising: forming a SiGe film on each of the flattenedsidewalls of the Si mesa structure; performing thermal oxidation to turnthe Si mesa structure and the SiGe film into a SiGe mesa structure andsilicon oxide film, the silicon oxide film covering sidewalls of theSiGe mesa structure; and removing the silicon oxide film, being carriedout prior to the forming the gate insulating film.
 23. The methodaccording to claim 19, wherein the mesa structure having the flattenedsidewalls is made of Si, the method further comprising: forming a SiGefilm on each of the flattened sidewalls of the Si mesa structure;performing thermal oxidation to turn the Si mesa structure and the SiGefilm into a SiGe wire structure and a silicon oxide film, the siliconoxide film covering the SiGe wire structure; and removing the siliconoxide film, being carried out prior to the forming the gate insulatingfilm.
 24. The method according to claim 19, wherein the heat treatmentin the hydrogen atmosphere is carried out at a temperature between 950°C. and 1100° C. with a hydrogen partial pressure of 0.2×10⁵ Pa orhigher.
 25. A method for manufacturing a field effect transistor,comprising: forming a mask comprising an insulating film on asemiconductor layer containing Si, the semiconductor layer being formedon a semiconductor substrate; forming the semiconductor layer into a Simesa structure by performing etching with the use of the mask, the Simesa structure having a pair of sidewalls extending in a first directionparallel to an upper face of the semiconductor substrate, the sidewallsfacing each other; reducing a distance between the sidewalls to be lessthan a width of the mask in a second direction perpendicular to thefirst direction and flattening the sidewalls by performing a heattreatment in a hydrogen atmosphere, the flattened sidewalls being formedwith one of a {110} plane or a {111} plane; forming a SiGe film on eachof the flattened sidewalls of the Si mesa structure; performing thermaloxidation to turn the Si mesa structure having the flattened sidewallsand the SiGe film into a SiGe mesa or wire structure and a silicon oxidefilm, the silicon oxide film covering sidewalls of the SiGe mesa or wirestructure; and removing the silicon oxide film, forming a gateinsulating film covering the flattened sidewalls; forming a gateelectrode covering the gate insulating film; and forming source anddrain regions on two sides of the gate electrode.
 26. The methodaccording claims 25, wherein: the semiconductor substrate is a bulk Sisubstrate having a {001} plane as a principal surface; and each of theflattened sidewalls of the mesa structure is formed with a {110} plane,and a connecting portion between each of the flattened sidewalls and theSi substrate have a {111} plane as a surface.
 27. The method accordingto claim 25, wherein the heat treatment in the hydrogen atmosphere iscarried out at a temperature between 950° C. and 1100° C. with ahydrogen partial pressure of 0.2×10⁵ Pa or higher.